A conditioned stimulus is previously neutral stimulus that, after becoming associated with the unconditioned stimulus, eventually comes to trigger a conditioned response.
Related terms
Conditioned Response: This is the learned reaction to the conditioned stimulus. In our analogy above, feeling hungry when hearing the special ringtone would be your conditioned response.
Stimulus Generalization: This is when an organism responds in a similar way to different but related stimuli. For example, if you started feeling hungry when hearing any phone ring after conditioning.
Stimulus Discrimination: This is when an organism learns to respond differently to various stimuli that are similar. For example, only responding (feeling hungry) to your specific pizza-ringtone and not other ringtones.